1. Field of the Invention
This invention relates to rotatable assemblies for supporting and/or positioning work pieces for manufacture, transfer or assembly; and more particularly to such assemblies which are peripherally supported and non-centrally driven by drive means inboard of the platform.
2. Description of Related Art
Rotating tables, platforms, or assemblies that provide component or work piece support, positioning, and transfer are used in manufacturing, material handling and assembling processes. One type of such assembly is known as a turntable or indexing table which can selectively accommodate different types of tooling or work pieces which are moved into precise position, for example, proximate a work station. Rotating platforms or table assemblies, which rotate about a vertical axis, are typically used in manufacturing, material handling, and assembly processes to move articles such as components, fixtures, work pieces, tooling and the like through precisely defined rotational angles in a plane substantially parallel to the table surface.
With the need for very precise machining and close tolerances in manufacture, turntables have had to be much more precise and provide more through-put in order for industry to remain competitive. Turntables, for example, may be required to move through a complex set of rotary profiles such as continuous rotation, indexing with a dwell time, oscillation, variable speed or reverse direction. It would be advantageous to have an assembly capable of all these motions while maintaining precision. In addition, with the advent of robotics these assemblies are required to place a workpiece at various work angles relative to the work station to provide access from automated operational equipment.
Typically, prior art turntables or indexing tables are centrally driven and work is performed at the periphery of the table. Because of the distance from the workpiece to the central support, extreme moments and forces on the drive mechanism are created. The drive system design must accommodate high torque and energy requirements, thus increasing the size and cost while diminishing the precision of the drive system.
The limitations of such assemblies are exacerbated where both the support and the drive system are located near the center of the table. Both the drive and support system are subjected to large moment loads exerted by the table mass in conjunction with external loads applied toward the periphery of the table by manufacturing or assembly operations. As a result, the tables have had to be more or less solid and sufficiently thick to minimize deflection at their periphery. This has resulted in even greater mass requirements, subjecting the drive and support systems to even greater loads and increasing inertia. Thus, greater energy is required to drive the table, start and stop it, or reverse direction.
Additionally, with the advent of robot aided and multidimensional work operations to be performed at a particular station, the necessity for these platforms to be positioned, lifted and canted in various orientations has become heightened. Further, with multifaceted workstations, angles of attack for assemblies and tools have become more critical, requiring positioning of robots and tooling at other than single locations. Because of the preciseness of the operations to be performed at a particular work station, the indexing and rotational positioning of such tables has become hypercritical. Additionally, the use of large mass, centrally driven assemblies precludes the use of, for example, centrally mounted robots or the use of two tables, one inside the other, offset in a manner to allow a spaced relationship of work pieces and/or assemblies and manufacturing mechanisms.
Alternately, when tables are driven on their outside diameter, the drive mechanism tends to be outside the periphery of the table and thus impedes use of the assembly in various angles and in operations where space is at a premium. Additionally, this configuration interferes with operations to be performed with large overhanging work pieces. Thus, for example, in operation where apparatus is necessary in close proximity to platform and space at the periphery is at a premium, it would be useful to have an assembly wherein the entire drive mechanism could underlay the support structure and avoid protruding into the space around the periphery of the platform yet not be centrally driven. Further, it would be advantageous to have a table or platform wherein tooling and/or fasteners such as hooks or the like could be fastened directly to the peripheral edge of the assembly. With peripheral driven mechanisms this is not possible.
Assemblies which contains the drive means outside the periphery of the platform suffer numerous other disadvantages. Specifically, these exposed drive mechanisms are subject to the operating environment of the work. Thus, fluids, tailings, chips and other contaminants can damage the mechanism or otherwise render it inoperable. Additionally, platform support bearings mounted inboard of the drive mechanism are more difficult to service and maintain. Out board mounted drive mechanisms also create a hazard to workers in the area.
It would be highly desirable to have a platform or table which could be very precisely positioned at any angle in order to accommodate multifaceted angles of operation as well as providing a lightweight, versatile, open center configuration such that more than one table can be offsettingly positioned, one inside the other, to provide spacing for robotics at center positions within the platform without the drive mechanism interfering. Further, it would be advantageous to provide a platform which is movably supported and driven proximate the work piece such that torques and loads applied at a work station are absorbed proximate their application without creating large moment arms. Further, it would be advantageous to drive the platform from beneath such that neither the motor or the actual driving mechanism was exposed yet the drive mechanism was disposed proximate the platforms outer rim for driving accuracy and reduction of forces required for movement but was not on the outside perimeter of the platform where it could snag, catch or rub. Further, it would be advantageous to have such an assembly which is lightweight, is relatively inexpensive when considered against the centrally driven tables, requires less energy and provides easy maintenance, flexibility and better access to the work piece at a work station.
While some attempts have been made to overcome these difficulties individually, no present system overcomes all the limitations discussed and provides all the desired attributes. By way of example, the limitations of the prior art are shown in U.S. Pat. No. 5,201,249 to Sterenberg which discloses a system utilizing a center drive shaft and bearing system. The system attempts to achieve greater versatility by incorporating a second drive shaft driven by a second motor within a hollow first drive shaft driven by a first motor so that a second table, mountable to the second drive shaft, can be rotated in a different motion from a first table mounted to the first drive shaft. U.S. Pat. No. 2,965,208 to Forster discloses a system utilizing a central shaft operably connected to its drive to rotate the table. The table also supports a plurality of rotatable spindles separately driven to accommodate actions requiring rotation of the work piece at an indexed position of the table. U.S. Pat. No. 5,170,678 to Wawrzyniak discloses an index table which utilizes a table top having an open center and ring gear/pinion gear drive system located beneath the rim of the table top. The table top is supported on a fluid (air or oil) cushion during rotation. After the position is indexed, the cushion is removed and the table top lowered by gravity into place on a fixed support. While suited for its intended purpose, this assembly still suffers from the limitations here discussed and is not readily adaptable for operation in a variety of orientations. A commercial assembly marketed by Camco utilizes a shaft-driven cam to drive an index table wheel having a center hole and supported by a bearing system located beneath it. This system is also limited in its operational versatility, is still weighty, and does not minimize energy requirements. It would therefore be advantageous to have an assembly wherein the entire drive mechanism could underlay the support structure and avoid protruding into the space around the periphery of the platform. Further, it would be advantageous to have a table or platform wherein the rotatable support and the drive was proximate the work load on the platform to provide better stability and accuracy and wherein tooling and/or fasteners such as hooks or the like could be fastened directly to the peripheral edge of the assembly. With peripheral driven mechanisms this is not possible.